Energy-efficient tunnel ventilation device

ABSTRACT

A ventilation device that enhances the effective longitudinal thrust of a fan assembly installed within a tunnel, by turning the discharged flow away from the surrounding tunnel surfaces and tilting the nozzle trailing edge ( 6 ) so that it forms an angle ( 16 ) to the nozzle centreline ( 8 ).

BACKGROUND OF THE INVENTION

Longitudinal ventilation via jetfans is generally acknowledged as beinga cost-effective solution for tunnels, where the length and risk profileof the tunnel allows such an installation. However, jetfans are notparticularly energy efficient, with typical installations wasting overhalf the supplied electrical power.

A major reason for the inefficiency of jetfans is the Coanda effect.This causes the stream of high-velocity air issuing from a jetfan toadhere to adjacent solid surfaces including the tunnel wails and soffit.A significant proportion of the aerodynamic thrust, typically 20% to30%, is thereby wasted through the friction between the jet and thesurrounding tunnel surfaces.

A previous patent GB2465261 granted to the present Applicant describesconvergent nozzles that can be installed on one or both sides ofjetfans, in order to accelerate the tunnel air and turn it away from thetunnel surfaces. In practice, this invention has been implemented byfitting conical nozzles onto jetfans.

The fitting of convergent nozzles onto jetfans does however come with anenergy performance penalty where such nozzles are fitted to the inletside of a reversible jetfan. The reason for this is that the powerabsorbed due to the inlet-side pressure drop cannot be recovered. Thisis contrary to the exit side where the kinetic energy of the dischargedair serves to accelerate the tunnel air.

In order to reduce the inlet pressure losses to jetfans, circularbellmouths are typically fitted to the inlet side, in order to ensure asmooth flow. For reversible flow jetfans, such bellmouths are typicallyfitted to both sides of the jetfan. Due to manufacturing reasons,bellmouths are generally spun from sheet metal into a circular shape.The circularity of the bellmouths introduces a significant constraint onthe shape of a jetfan nozzle. In particular, it has not previously beenpossible to combine the advantages relating to a reduction of the Coandaeffect through the fitting of convergent nozzles with low inlet flowlosses into a jetfan.

JP-A-H1-237400 discloses a jetfan with an undercut on the lower side ofthe cylindrical casing, to encourage the discharged air to turn awayfrom the tunnel soffit.

JP01130099A discloses an arrangement with multiple fans connected inparallel, delivering flow to a common plenum which in turn supplies airto a nozzle fitted with turning vanes. This complex arrangement is notsuitable for most tunnels, which are ventilated using individualjetfans.

Neither JP-A-H1-237400 nor JP01130099A discloses a system that ispractical or efficient. The Applicant believes that there remains scopeto improve the energy efficiency of longitudinal tunnel ventilationsystems.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a fanassembly for installation in a tunnel to provide ventilation in thetunnel, the fan assembly comprising:

-   -   a fan rotor for generating a ventilating flow; and    -   the inflow into the fan rotor being substantially parallel to        the outflow from the fan rotor;    -   a nozzle coupled to the fan, the nozzle having a trailing edge        at the distal end from the fan; and    -   wherein the assembly is arranged or arrangeable such that a        ventilating flow generated by the fan will pass through the        nozzle before exiting the assembly to enter a tunnel to be        ventilated; and    -   the nozzle being arranged to turn the flow away from the        surrounding tunnel surfaces, in that at least one edge of the        nozzle throughbore is at an angle to the fan centreline; and    -   wherein the angle made between the nozzle trailing edge and the        centreline of the nozzle is within the range of 45 degrees to 85        degrees.

The flow through a jetfan is driven by an axial fan, which gives animpulse to the tunnel airflow. The invention provides a solution to thetechnical issue of how to turn the flow from a jetfan away from thesurrounding tunnel surfaces and hence achieve greater in-tunnelaerodynamic thrust, without choking the flow through the jetfan throughincreased pressure losses.

According to a further aspect of the invention, there is provided a fanassembly for tunnel ventilation, the assembly comprising:

-   -   a fan for generating a ventilating flow in a first direction;        and    -   a nozzle adjacent to the fan in the first direction so that the        ventilating flow will pass through the nozzle before exiting        into a tunnel to be ventilated;    -   wherein the nozzle has a first end proximal to the fan and a        second end distal from the fan having a trailing edge, the angle        between the trailing edge and the nozzle centre line is        substantially within the range of 45 to 85 degrees and the        nozzle is arranged to direct the ventilation away from        surrounding tunnel surfaces.

This aspect of the invention is achieved by tilting the trailing edge ofthe nozzle, so that one side of the nozzle (the ‘pressure side’) islonger than the opposite side (the ‘suction side’). The pressure side ofthe nozzle is termed thus because when the nozzle is placed on thedischarge side of the jetfan, the pressure side ‘pushes’ the airflowaway from the tunnel surrounding surfaces when the jetfan is in use. Thepressure side would thus experience a static pressure that is greaterthan that on the opposite suction side.

In case a convergent nozzle is used as described in patent GB2465261,tilting the trailing edge of the nozzle has the effect of increasing theaerodynamic throat of the nozzle, and hence reducing the pressure dropthrough the nozzle throughbore. The power consumption of the jetfan isthus significantly reduced.

The range of angles between the trailing edge and the nozzle centre linehas been selected on the basis of experimental evidence with the design,manufacture and testing of such jetfans. For a typical overall nozzlelength to fan diameter ratio of unity and a circular trailing edge ofthe same diameter as the fan, the lower value of 45 degrees for theangle between the trailing edge and the nozzle centre line correspondsto a throughbore to fan area ratio of approximately 1.4, which wouldsignificantly choke most jetfan impellers. The higher value of 85degrees for the angle between the trailing edge and the nozzle centreline corresponds to the minimum change from a conventional jetfan nozzlearrangement that our experience indicates would be commerciallybeneficial to produce.

In practice, manufacturers stock a standard range of bellmouths. Thepresent invention permits the selection of a standard bellmouth sizewhich can be installed at a tilt to the nozzle centre-line. Inparticular, a bellmouth with the same nominal diameter as the fan onwhich the nozzle is to be installed can be used. This option to usestandard jetfan parts is a key advantage of the present invention.

The nozzle can typically be used for acoustic silencing, as well as forturning the discharged flow away from the tunnel surrounding surfaces.From previous laboratory measurements, it has been established that theperformance of the silencer is dependent upon the solid angle subtendedby the silencer surface onto the fan outlet. Through judicious choice ofnozzle geometry, adequate acoustic silencing can be achieved, given theocclusion of the fan outlet by the nozzle ‘pressure side’.

The arrangement of the circular fan outlet connected to a tiltedbellmouth typically leads to a non-conical shape for the nozzle, and acomplex developed shape for the nozzles skins is required for sheetmetal cutting. The shape of the proposed nozzle is thus different fromthe shapes envisaged in GB2465261 and JP-A-H1-237400. In the case of thelatter reference, since the nozzle trailing edge is shaped as anellipse, it is not feasible to attach bellmouths on the nozzle trailingedges, which in turn implies significant pressure losses. In addition,the nozzle is straight and hence there is no effective turning of thedischarged air. That prior art design therefore does not provide apractical or efficient solution for tunnel ventilation.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of preferred embodiments of the present invention will now bedescribed by way of example only, and with reference to the accompanyingdrawings, in which:

Like reference numerals are used for like components throughout thefigures;

FIG. 1 shows an embodiment of a ventilation apparatus with nozzles asdescribed in this invention installed on both sides of a fan;

FIG. 2 shows an end view of a ventilation apparatus with a nozzle asdescribed in this invention;

FIG. 3 shows an embodiment of a ventilation apparatus with a nozzle asdescribed in this invention installed on one side of a fan.

FIG. 4 shows a typical flat developed pattern for a nozzle skin which isto be cut from sheet metal.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring to FIG. 1, this shows a side view of an embodiment of thepresent invention within a bidirectional ventilation apparatus, which isdesigned to operate in a fully reversible manner.

In this embodiment, a fan assembly comprising a fan rotor (3) driven bya motor (4) is installed within a fan housing (15). Airflow (5) entersthe fan rotor (3) through a bellmouth (1) and an inlet nozzlethroughbore (10A), before being discharged thorough an outlet nozzlethroughbore (10B).

As can be seen in FIG. 1, the nozzle has a centreline (8), defined asthe geometric mean between the pressure side (11) and suction side (12)lines. An angle (13) is defined between the fan centreline (7) and thenozzle centreline (8). The pressure side of the nozzle (11) is arrangedto turn the flow direction, so that in use, the discharged air flowsaway from the surrounding tunnel surfaces.

A further angle (16) is defined between the nozzle centreline (8) and atrailing edge (6) of the nozzle. Preferably, the angle (16) is between45 degrees and 85 degrees. Preferably still, the angle (16) isapproximately 65 degrees.

The embodiment of FIG. 1 shows a nozzle pressure side angle (17) of 7degrees. A larger geometric throat (14) can be arranged at both theinlet and discharge sides of the nozzle, by tilting the nozzle trailingedge (6) by the angle (16) between the nozzle centreline (8) and thetrailing edge (6). This leads to reduced pressure losses and improvedenergy efficiency.

It is possible to arrange the length of the suction side to beapproximately equal to one fan diameter, and selecting the pressure sideangle (17) to be 6 degrees. This preferred embodiment provides anenhanced level of acoustic attenuation compared to the embodimentdescribed in FIG. 1.

FIG. 1 shows a preferred embodiment where the suction side of the nozzlethroughbore (12) is arranged to be parallel to the fan centreline (7).

Referring now to FIG. 2, which shows an end view of an embodiment ofthis invention, the nozzle shape is arranged to turn to flow in aprescribed direction, preferably away from the surrounding tunnelsurfaces.

FIG. 2 shows that the nozzle trailing edge is circular in shape, toallow attachment to a circular bellmouth. Such a circular bellmouthsignificantly reduces the inlet pressure drop.

We refer now to FIG. 3, which shows a side view of a particularembodiment of this invention which would normally (but not exclusively)be operated in a unidirectional manner.

In this embodiment, the indicated airflow direction is from left toright, i.e.

the airflow enters into a straight nozzle via a bellmouth (1) first,prior to being accelerated by the fan rotor (3) into a shaped nozzlewith a throughbore (10). The discharged flow is turned by a pressureside (11) which is longer than the suction side (12), such that in use,the discharged air flows away from the surrounding tunnel surfaces.Since a straight inlet nozzle is selected in this embodiment, the inletpressure drop to the fan is less than that for the embodiment depictedin FIG. 1. The aerodynamic thrust can therefore be expected to be higherfor the embodiment described in FIG. 3 compared to that in FIG. 1.

In FIG. 3, the flow direction can if necessary be reversed by runningthe fan rotor in the opposite direction. Due to the increased Coandaeffect and additional inlet pressure drop, a reduction of the in-tunnelaerodynamic thrust can be expected in the reverse flow direction (i.e.from right to left) in the embodiment described in FIG. 3.

It would be possible to modify an existing fan assembly in order to fitnozzles as described in this invention to one or more sides of a fan,and hence reap the benefits of improved performance.

There are no restrictions on the degree of divergence or convergence ofthe throughbore area with this invention. In particular, the throughboreareas at the inlet and discharge can be arranged to be equal to, orgreater than, the fan area. Depending on the fan flow characteristics,this flexibility can increase the efficiency of the fan assembly. Thepresent invention relieves the ‘choking’ of the inlet flow which can bepresent in GB2465261, and thus delivers a significant improvement in fanperformance.

FIG. 4 shows the flat developed pattern for a nozzle skin which is to becut from sheet metal, for the jetfan depicted in FIGS. 1 and 2. Thepresent invention requires a single direction of curvature for thenozzle skins, and the nozzle skins can therefore be developed from aflat sheet without the need for stretching. The topology of the nozzleskins in this invention is therefore particularly suitable forsheet-metal manufacture.

The manufacturability and cost-efficiency of the nozzles in thisinvention have been proven through production trials. It has been foundthat the nozzle skin can be rolled from a single flat sheet of metal forsmall fan diameters (around 500 mm), while separate sections of nozzleskin, each rolled from a flat sheet, are required for larger fandiameters of up to 2 m. Both the inner and outer nozzle skins can berolled into the requisite shapes, with acoustic material insertedbetween them for sound attenuation during fan operation.

It will be appreciated that the foregoing are merely an examples ofembodiments and just some examples of their use. The skilled reader willreadily understand that modifications can be made thereto withoutdeparting from the true scope of the inventions.

1. A fan assembly for installation in a tunnel to provide ventilation in the tunnel, the fan assembly comprising: a fan rotor for generating a ventilating flow; and the inflow into the fan rotor being substantially parallel to the outflow from the fan rotor; and a nozzle coupled to the fan, the nozzle having a trailing edge at the distal end from the fan; and the assembly being arrangeable such that a ventilating flow generated by the fan will pass through the nozzle before exiting the assembly to enter a tunnel to be ventilated; and the nozzle shape being arranged to turn the flow away from the surrounding tunnel surfaces, in that at least one edge of the nozzle throughbore is at an angle to the fan centreline; and wherein the angle made between the nozzle trailing edge and the centerline of the nozzle is within the range of 45 degrees to 85 degrees.
 2. A fan assembly with a nozzle as described in claim 1, wherein the nozzle trailing edge forms the shape of a circle.
 3. A fan assembly with a nozzle as described in claim 1, wherein at least one edge of the nozzle throughbore is parallel to the fan centreline.
 4. A fan assembly with a nozzle as described in claim 1, wherein a bellmouth is attached to the nozzle edge.
 5. A fan assembly with two nozzles as described in claim 1, with one nozzle installed on each side of a fan. 6-8. (canceled) 